Starting in approximately 1984, low cost personal laser printers became available. All dry electrophotographic copiers and printers develop an image utilizing a dry toner. The typical toner is composed of styrene acrylic resin, a pigment-typically carbon black, and a charge control dye to endow the toner with the desired tribocharging properties for developing a latent electrostatic image. Styrene acrylic resin is a thermo-plastic which can be melted and fused to the desired medium, typically paper.
For a dry electrophotographic system to operate worldwide it must be able to operate satisfactorily on AC power systems providing from 90 Vrms to 240 Vrms at frequencies of 50 Hz to 60 Hz. The AC power operates two major sub-systems within the electrophotographic system. A switching power supply supplies power for the electronics, motors and displays. Power requirements for the switching power supply varies, but is generally under 100 watts. The second major sub-system in an electrophotographic system is the fusing system. The typical fusing system is composed of two heated platen rollers which, when print media with a developed image pass between them, melt the toner and through pressure physically fuse the molten thermal plastic to the medium. Heating is usually accomplished by placing a high power tungsten filament quartz lamp inside the hollow platen roller. As with the switching power supply, the fusing system power requirement varies between printers but is on the order of 1,000 watts.
The combination of the electrophotographic printer, switching power supply, fusing system and power electronics when must meet International Electrical Commission (IEC) regulations IEC 555-2 and IEC 555-3 for current harmonics and flicker. The printer must pass Federal Communications Commission (FCC) class B regulations for power line conducted emissions and radiated emissions. In addition, the printer must pass CISPR B requirements for power line conducted emissions and radiated emissions. Finally, the printer must not suffer from excessive acoustic multi-tone or single tone emissions in the human auditory range in the office environment. The electrophotographic system must be capable of switching into a power down or power off mode for energy savings as suggested by the EPA Energy Star Program.
Prior to the present invention, a power factor correction type switching power supply most commonly has a boost regulator situated in the "front end" to pre-regulate and shape the waveform of the current so that it is close to a sinusoid and in phase with the input voltage. Such an arrangement may have considerable power conversion losses. Additionally, the cost of the additional electronics required for the boost converter adversely impact the overall cost. Other solutions consisted of a power factor correction type switch mode power supply connected to the AC power source in parallel when a standard triac based fuser controller, which had very good power factor but suffered from excessive flicker and did not possess a universal fuser.